1. Field of the Invention
The present invention relates to a capacitive occupant sensor and a capacitive occupant detection apparatus.
2. Description of the Related Art
An occupant detection system is used for detecting a seating state of a seat of a vehicle such as whether an adult sits on the seat or a child sits on the seat.
Japanese Patent No. 3,739,930 discloses an occupant detection system in which a plurality of antenna electrodes is symmetrically arranged in a seat cushion so as be separated from each other. An area opposing the antenna electrodes is different between when an adult sits on the seat and when a child sits on the seat. The occupant detection system compares electric current that flows among the antenna electrodes and a threshold value and thereby determining whether an occupant sitting on the seat is an adult or a child.
The occupant detection system detects electric current that flows in the antenna electrodes in accordance with an opposing area of an occupant and the antenna electrodes. Thus, a difference in outputs from the antenna electrodes becomes small between a case where a small adult corresponding to an AF05 dummy sits on the seat and a case where a large adult corresponding to an AM50 dummy sits on the seat. Therefore, the occupant detection system is difficult to discriminate between a small adult and a large adult.
U.S. Pat. No. 4,796,013 (corresponding to JP-A-62-225985) discloses an occupant detection apparatus in which a sensing electrode is disposed on wadding made of an insulator, as a seat cushion trim cover for providing an outer, cloth of the seat, and the sensing electrode is disposed between the outer cloth and the wadding. The sensing electrode is used as an electrode for a variable capacity capacitor and is electrically coupled with an oscillator. The occupant detection apparatus detects an occupant based on a capacity of the variable capacity capacitor. The occupant detection apparatus is also difficult to discriminate between a small adult and a large adult.
US 2003/0090376 A1 (corresponding to JP-A-2003-232866) discloses an occupant detection system in which an occupant detection sensor is disposed on a sheet-shaped insulator. The occupant detection sensor is coupled with a control device for detecting characteristics and existence of an occupant. The control device detects an occupant based on a signal from the occupant detection sensor. The occupant detection system is also difficult to discriminate between a small adult and a large adult.